1. Field of the Invention
The invention relates generally to controlling the apparent curvature of turbine fan diffuser vanes to fan air flow by selective discharge of pressurized fluid, such as compressed air, from the surface thereof to prevent stalling of the vanes over a wider range of fan output than is possible with presently known mechanical adjustments. It has use in ride control systems for surface effect ships.
2. Brief Description of the Prior Art
It is known in the prior art to angularly adjust diffusers on the discharge side of centrifugal fans to maintain efficiency over a wide range of operating conditions. Examples of mechanically adjusted diffusers are taught, for example, in U.S. Pat. Nos. 2,341,974; 2,797,858; 2,985,427; and 3,957,392.
It is also known in the prior art to vary the physical shape of diffuser vanes in centrifugal compressors by admitting pressure to inside the vane, thus employing the principle of the Bordon tube. This is taught in U.S. Pat. No. 2,323,941. An arrangement employing boundary layer control over diffuser vanes is disclosed in U.S. Pat. No. 2,084,463 where downstream air is directed to and discharged from the surface of diffuser vanes located upstream. U.S. Pat. No. 3,172,495 illustrates the use of air discharge from airfoil members to laterally deflect a moving stream of air. Circulation of air over a wing surface involving the Coanda effect for lift control is shown in U.S. Pat. Nos. 3,016,213 and 3,830,450.
In U.S. Pat. No. 2,830,754 there is taught in the axial compressor art the reverse flow of a small quantity of pressurized air from hollow stator vanes in a high pressure section of the compressor to hollow stator vanes in a lower pressure section. From there it is discharged to the surface of the vane so as to control the direction of flow of the compressed air to the next row of rotor vanes.